1. Field of the Invention
The present invention generally relates to a memory unit which records or reproduces to-or-from a storage medium through a plurality of heads, and more particularly, to a memory unit in which a head assembly having the plurality of heads is connected with a printed circuit board having control circuits through lines.
2. Description of the Prior Art
Recently, electronic devices have been further miniaturized, and it is desired to also miniaturize a memory unit used for an external storage unit of a computer, etc. More specifically, in a magnetic disk unit which records and reproduces to-and-from a storage medium through a plurality of heads assembled in a head assembly, the number of lines connected between the head assembly and a printed circuit board having control circuits needs to be reduced.
FIG. 1 shows a schematic block diagram of an interface circuit of a conventional magnetic disk unit. A magnetic disk unit 11 shown in FIG. 1 comprises a head assembly 12 for assembling a plurality of heads, a printed circuit board 15 for controlling the head assembly 12, and a plurality of lines connecting between the head assembly 12 and the printed circuit board 15.
In the head assembly 12, differential-type heads 13-1 to 13-16 for recording and reproducing to-and-from a plurality of magnetic disks are assembled. Included in the head assembly 12 is a head IC 14, which selects one of the heads 13-1 to 13-16, and transmits-and-receives write-data/and/read-data. The head IC 14 is also fabricated on a flexible printed circuit board.
On the other hand, the plurality of lines between the head assembly 12 and the printed circuit board 15 comprise twelve lines which include, four head-selection signal lines 16-1 to 16-4, write-data signal lines 17-1, 17-2, read-data signal lines 18-1, 18-2, a write-gate signal line 19, a ground (GND) line 20, and two-types (12 V and 15 V) power-supply lines 21-1, 21-2.
These signal line are constructed by flexible print circuits (FPC) or flat cables, etc., between the printed circuit board 15 and the head assembly 12.
For selecting one of the sixteen heads 13-1 to 13-16, four-bit signals are needed. The above four head-selection signal lines 16-1 to 16-4 are set for these four-bit signals. In this way, a number of the head-selection signal lines is determined by a number of bits necessary for selecting one of heads.
FIG. 2 shows a connecting configuration of the interface circuit in the conventional magnetic disk unit shown in FIG. 1. In an example shown in FIG. 2, the head assembly 12 is installed such that the sixteen heads 13-1 to 13-16 are close to magnetic disks 22-1 to 22-8. Each of these heads 13-1 to 13-16 is mounted at the top of suspension gimbals 24 connected with a carriage 23 and can be moved in a radial direction of the magnetic disks 22-1 to 22-8.
Two signal lines from each of the heads 13-1 to 13-16 are connected to associated pattern lines 26 on the flexible printed circuit board 25 through the suspension 24 and the carriage 23. Each of the pattern lines 26 on the flexible printed circuit board 25 are routed to ports of the head IC 14 mounted thereon.
On the other side of the head IC 14, each port of the head IC 14 is connected to an associated port of one side of an FPC 27. Also on the other side of the FPC 27, a connector 28a is assembled. In the FPC 27, the above mentioned twelve lines, 16-1 to 16-4, 17-1, 17-2, 18-1, 18-2, 19, the GND line 20, and the power-supply lines 21-1, 21-2, are formed by patterns 27a. Thick lines of the patterns 27a are allocated to the GND line 20 and the power-supply lines 21-1, 21-2.
On the other hand, the printed circuit board 15 for controlling and driving the magnetic disk unit 11 comprises a connector 28b, which is connected with the connector 28a, so as to connect between the printed circuit board 15 and the head assembly 12.
To miniaturize the magnetic disk unit 11, the number of lines between the printed circuit board 15 and the head assembly 12 also needs to be reduced. For this purpose, an example of reducing the number of connection lines by transmitting data in series is disclosed in Japanese Laid-open Patent No. 6-30505. In this example, a system, in which a main control unit is connected with a peripheral unit through a single data signal line and a single clock signal line, is disclosed. In this system, during one serial transmission, "information of data-transmit/receive directions", "information of a data type", and "information of data" are transmitted and received in that order.
To miniaturize the magnetic disk unit 11, the width of the FPC 27, namely the width of each pattern 27a, needs to be thinner. However, reducing the width of the pattern 27a any more causes noise due to voltage fluctuation. There is thus a problem that it is hard to miniaturize recording-and-reproducing units, such as a magnetic disk unit by thinning the width of each pattern 27a of the FPC 27.